send(body) {
    if (this._ws.readyState === 1) {
        this._ws.send(body)
    } else {
        setTimeout(() => {
            this._ws.send(body)
        }, 1000)
    }
}

on(event, cb) {
    if (event && typeof cb === 'function') {
        /**
         * @event response: param is jsonrpc message
         * @event error: param is jsonrpc message
         * @event success: param is jsonrpc message(object)
         * @event downInit: param is gid
         * @event downError: param is gid
         * @event downStatus: param is result(object with gid)
         * @event downInfo: param is result(object with gid)
         * @event downComplete: param is gid
         */
        this._emt.on(event, cb)
    }
}

addUri(url) {
    if (isURL.test(url)) {
        let req = {
            params: [this.secret, [url]],
            jsonrpc: '2.0',
            id: 'Init',
            method: 'aria2.addUri'
        }
        this.send(JSON.stringify(req))
    } else {
        throw Error('invalid url')
    }
}

getFiles(gid) {
    if (gid) {
        let req = {
            params: [this.secret, gid],
            jsonrpc: '2.0',
            id: `Info.${gid}`,
            method: 'aria2.getFiles'
        }
        this.send(JSON.stringify(req))
    }
}

tellStatus(gid) {
    if (gid) {
        let req = {
            params: [
                this.secret,
                gid,
                [
                    'gid',
                    'status',
                    'totalLength',
                    'completedLength',
                    'errorCode',
                    'errorMessage',
                    'dir'
                ]
            ],
            jsonrpc: '2.0',
            id: 'Status',
            method: 'aria2.tellStatus'
        }
        this.send(JSON.stringify(req))
    }
}

parseResponse(res) {
    try {
        res = JSON.parse(res)
    } catch (error) {
        throw Error('invalid response')
    }
    this._emt.emit('response', res)
    if (!isObject(res) || res.hasOwnProperty('error')) {
        //error response
        this._emt.emit('error', res)
    } else {
        //success response
        this._emt.emit('success', res)
        if (res.hasOwnProperty('id')) {
            //a request-response mapping pair
            switch (res.id.split('.')[0]) {
                case 'Init':
                    this._emt.emit('downInit', res.result)
                    break
                case 'Status':
                    this._emt.emit('downStatus', res.result)
                    break
                case 'Info':
                    let { completedLength, length, path } = res.result[0]
                    this._emt.emit('downInfo', {
                        gid: res.id.split('.')[1],
                        path,
                        completedLength,
                        totalLength: length
                    })
                    break
            }
        } else {
            //a notification from server, has method, param as data
            switch (res.method) {
                case 'aria2.onDownloadError':
                    this._emt.emit('downError', res.params[0].gid)
                    break
                case 'aria2.onDownloadComplete':
                    this._emt.emit('downComplete', res.params[0].gid)
                    break
            }
        }
    }
}

getData(gid) {
    return this._gd[gid] || {}
}